Family: His mother was house keeper for the rich Okudaira family, and lived in their mansion (in Haido district) with Eisuke. During this time, Hidemi Hondou, his elder sister, was said to have been studying abroad, and his dad, Ethan Hondou, to be working in Osaka. When his mother died, nearly 10 years before canon (Eisuke: 7 or 8), Eisuke went to live with his father for a couple of years. After this, Ethan went "overseas" and since, Eisuke has been living with one of Ethan's friends, receiving an allowance.

So Mom dies when Eisuke is around 7 or 8, Sis vanishes shortly after, and Dad "vanishes" when he is 13/14.

Dad is in fact *dead*, the BO believe Kir killed him (4 years ago), in truth, Ethan arranged for Kir/Rena/Hidemi to appear to have killed him, while he shot himself telling her what to say and to take over his mission, all to save her life.

Ethan was a CIA agent who had infiltrated the Black Organisation.Hidemi became one too, and has been infiltrated in the BO for longer than she would have liked.

Eisuke comes to Tokyo to investigate this "Rena Mizunashi" who so looks like his sister. He suspects "Rena" is someone using Hidemi's face, and decides she is his only clue to finding Hidemi again. He then confronts her, finds out she is his sister, and then is basically told by Conan and FBI to go away, they have big fish to talk about. 8D

He is offered Witness Protection Program, but it appears he has/will(?) refused.

On his mother: "Your mother was such a wonderful house-keeper! She was considerate and always had a smile on her face..."

Eisuke's blood group is, at birth: OO, post surgery: AB+.Hidemi's blood group is AB+. She gave blood to Eisuke shortly after his arrival in Osaka, when he got into an accident.